Contribution to the Gametophyte Morphology of the Fern
Genus Lomagramma J. Sm. in India
Author(s): Subhash Chandra, Mrittunjai Srivastava, Ruchi Srivastava
Source: American Fern Journal, 93(1):25-31. 2003.
Published By: The American Fern Society
DOI: http://dx.doi.org/10.1640/0002-8444(2003)093[0025:CTTGMO]2.0.CO;2
URL: http://www.bioone.org/doi/
full/10.1640/0002-8444%282003%29093%5B0025%3ACTTGMO%5D2.0.CO
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American Fern Journal 93(1):25–31 (2003)
Contribution to the Gametophyte Morphology
of the Fern Genus Lomagramma J. Sm. in India*
SUBHASH CHANDRA and MRITTUNJAI SRIVASTAVA
Pteridology Laboratory, National Botanical Research Institute, Lucknow – 226001 (INDIA)
RUCHI SRIVASTAVA
Botany Department, Lucknow University, Lucknow – 226001 (INDIA)
ABSTRACT.—The gametophyte development of Lomagramma sorbifolia (Willd.) Ching has been
studied. Spore germination is of the polar and Vittaria-type. Prothallial development is either of
the Adiantum-type, or more rarely of the Drynaria-type. This Adiantum-type is unusual among
most of the other genera of the lomariopsidoid ferns. The Drynaria-type of gametophyte
development is more characteristic of the lomariopsidoid ferns. Older prothalli are cordate and
naked throughout. Early development seems to be somewhat plastic and perhaps of limited
usefulness as a character for systematic purposes.
Lomagramma J. Smith is a genus of about 15 species ranging from
northeastern India to Tahiti and into tropical America. It is represented by
a lone species, Lomagramma sorbifolia (Willd.) Ching, in India, where it is
known to occur in Garo Hills and Lakhimpur in the state of Assam (Chandra,
2000). The plants are scandent, large, terrestrial, and shade-loving growing
mostly near streams in dense tropical forests. The species is very similar to
Lomariopsis Fée and Stenochlaena J. Sm. in habit but has distinctive
bathyphylls and anastomosing veins.
Christensen (1938) considered the genus Lomagramma as acrostichoid,
probably of dryopteroid origin. Holttum (1947, 1949, 1954) for the first time
grouped the Lomariopsidoid genera in a separate sub-family Lomariopsidoideae under the family Dennstaedtiaceae. Alston (1956) raised the status of the
sub-family to the family level (Lomariopsidaceae), which was later followed by
Nayar (1974) and Pichi-sermolli (1877). Ching (1978) segregated Lomagramma
and Lomariopsis as an independent group constituting a separate family
Lomariopsidaceae (excluding other Lomariopsidoid ferns), possibly derived
from Bolbitidaceae.
Bower (1923–28) and Holttum (1949) pointed out that the comparative
morphology of fern gametophytes could be of significance in understanding
evolutionary relationships. According to Stokey (1951, 1960, 1964), Atkinson
and Stokey (1964), and Atkinson (1973) comparison of gametophyte structure
and their development strengthens our understanding of the relationships
among various genera and higher groups. They further indicated that useful
data might be found in spore germination pattern, the manner of cell plate
* NBRI Publication No. 515 (N.S.).
26
AMERICAN FERN JOURNAL: VOLUME 93 NUMBER 1 (2003)
development, meristematic region development, and in the type of early
prothallial development.
Morphologically, the family Lomariopsidaceae is poorly known except for
details regarding the sporophyte of Bolbitis and Egenolfia (Nayar, 1950, 1951,
1955, 1956, 1960, Nayar and Kaur, 1964), Elaphoglossum (Bell, 1950, 1951a,
1951b, 1955, 1956) and the rhizome morphology of Lomagramma sorbifolia
(Chandra, 1989).
Prothallial morphology in the family Lomariopsidaceae is known only
for Bolbitis (Nayar, 1960), Egenolfia (Nayar and Kaur, 1964, 1965), and
Elaphoglossum and Rhipidopteris (Stokey and Atkinson, 1957). Few details
are known about the gametophyte of Lomagramma sinuata (Atkinson, 1973).
The present study aims at describing the pathway of prothallus development
in L. sorbifolia and comparing that development with that seen in related ferns.
MATERIAL
AND
METHODS
The present study is based on material collected from Assam (S. Chandra,
LWG 12594). Fresh spores were surface sterilized with sodium hypochlorite
(2%) and thoroughly washed with sterilized water. The sterilized spores were
sown onto Petri dishes containing Parker and Thompson’s nutrient media
(Klekowski, 1969) jelled with 1% agar at 5.4 pH. The cultures were maintained at 22 6 28C under 600 ft. C. of light from four fluorescent lamps
placed horizontally above the culture dishes. All observations on morphology
and development of the gametophytes are based on these laboratory cultures.
To study cellular structure, the gametophytes were mounted in a 2% acetocarmine solution, which induced partial plasmolysis of the cells rendering the
cell outlines clear. Drawings were made using a camera lucida.
RESULTS
Spores are monolete, planoconvex to somewhat concavoconvex in lateral
view, having a granulose exine, devoid of perine (Nayar and Kaur, 1965) and
19 3 27 lm in size (average of 10 readings in each plane of spores selected at
random), swelling to 24.5 3 34 lm after acetolysis. They germinate within 15–
20 days of sowing. At germination an unequal division by a wall perpendicular
to the polar axis (parallel to the equatorial plane) of the spore delimits a large,
densely chlorophyllous, hemispherical prothallial cell from a small, lensshaped, and very sparsely chlorophyllous rhizoid initial cell next to the
proximal pole of the spore (Fig. 1). The rhizoid initial protrudes through the
laesural aperture and elongates parallel to the polar axis of the spore as
a slender, highly vacuolated rhizoid. Meanwhile, the prothallial cell enlarges,
elongating along the equatorial plane of the spore, splitting open the spore-coat
at the laesural region and dividing by a wall parallel to the polar axis
(perpendicular to the first wall) of the spore in such a way that the rhizoid is
attached laterally to the basal one of the two daughter cells (Figs. 2, 3); this
basal cell does not take any further part in prothallial development. Its sister
CHANDRA ET AL.: GAMETOPHYTES OF LOMAGRAMMA
27
FIGS. 1–29. Stages in the development of the gametophyte of Lomagramma sorbifolia. 1. Spore
germination. 2–3. Uniseriate germ filament. 4. Initiation of plate formation by oblique division of
the terminal cell. 8–9. Initiation of plate formation by vertical division of the terminal cell. 5–7 and
10–13. Germ filament showing early formation of apical cell. 14–15. Germ filament showing the
formation of a broad prothallial filament. 16. Branched germ filament. 17–25. Germ filament
showing establishment of apical cell. 26–27. Young gametophyte showing multicellular meristem.
28–29. Cordate gametophyte.
28
AMERICAN FERN JOURNAL: VOLUME 93 NUMBER 1 (2003)
cell elongates further along the equatorial plane and divides repeatedly by
walls parallel to its basal wall (parallel to the polar axis of the spore) forming
a short germ filament composed of short, barrel-shaped, and densely
chlorophyllous cells (Fig. 3). Spore germination, thus, is of the typical
Vittaria-type as described by Nayar and Kaur (1968, 1971), the first rhizoid
elongating along the polar plane of the germinating spore and the germ filament
elongating along the equatorial plane and perpendicular to the first rhizoid.
However, due to the physical obstruction provided by the spore coat, the
emerging germ filament is often slightly deflected from the equatorial plane.
When the germ filament is three to five cells long, formation of a prothallial
plate is initiated by an abrupt change in the plane of wall formation in the
terminal cell and often extending to the penultimate cell. Instead of dividing
by walls perpendicular to the long axis of the germ filament, these cells divide
by walls parallel to the long axis so that the germ filament at its anterior end
becomes two tired. Commonly the wall formed in the terminal cell is oblique
(Fig. 4) so that one of the daughter cells is larger with a broader anterior end.
Another wall oblique to this wall formed in the larger daughter cell delimits
a wedge-shaped apical meristematic cell (Figs. 5–7, 13). In some cases the first
division of the terminal cell is parallel (instead of oblique) to the long axis of
filament (Figs. 8, 9) followed by an oblique division in this cell to delimit
a wedge-shaped apical meristematic cell. Thus, a transverse row of three
daughter cells is formed, of which the middle one is wedge-shaped and acts as
a meristematic cell (Fig. 10). This type of prothallial development is termed the
Adiantum-type (Nayar and Kaur, 1969, 1971). The meristematic cell cuts off
a series of narrow daughter cells alternately against its oblique sides and these
daughter cells, by successive anticlinal and periclinal divisions, form an
expanded, one-cell-thick, obovate prothallial plate (Figs. 18–20). Daughter
cells of the meristematic cell grow and divide rapidly so that the anterior
region of the prothallus on either side of the meristematic cell progressively
extend anterior to the level of the meristematic cell, ultimately making the
young prothallus cordate (Figs. 28, 29).
A second abrupt change in the plane of cell divisions occurs in the apical
meristematic cell when the young prothallus is distinctly cordate. Instead of
dividing by walls parallel to its oblique sides, the apical cell divides by
a transverse wall, cutting off its wedge-shaped basal region from the larger
anterior region, which then divides repeatedly by longitudinal walls to form
a plate of 3 or 4 narrow cells. These cells constitute a pleuricellular meristem
(Figs. 26, 27) in which all cell divisions are longitudinal. Ultimately a central
midrib is established behind the meristem in the median plane of the thallus.
The prothallus becomes symmetrically cordate, and has semicircular lateral
wings (Fig. 28).
Occasionally, the establishment of an apical cell is much delayed. In such
cases the first division of the terminal cell is by a vertical wall (parallel to the
long axis of the filament instead of oblique) and soon a second wall is laid
down at a right angle to the first. A broad spatulate prothallial plate is formed
(Figs. 14–16) by divisions of the distal cells of the germ filament by walls
CHANDRA ET AL.: GAMETOPHYTES OF LOMAGRAMMA
29
parallel to the long axis and by repeated longitudinal and transverse divisions
in the daughter cells. This type of prothallial development is termed the
Drynaria-type (Nayar and Kaur, 1969, 1971). The plate often becomes 5–10
cells wide and broadly ovate but is devoid of any organized meristem (Figs. 17,
21–24). An obconical meristematic cell is differentiated later by two oblique
divisions in one of the marginal cells at the anterior end of the prothallial plate
(Figs. 25, 26). Finally, a symmetrical cordate prothallus is formed.
In a few cases the terminal cell of the germ filament may not participate in
the formation of the apical cell, or may be sluggish in doing so. In such cases,
the obconical meristematic cell is formed behind the terminal cell by an
oblique wall (Figs. 11, 12). Activity of this form of meristematic cell results in
a spatulate prothallial plate. The meristematic activity may be restricted to one
side of the plate, but ultimately an Adiantum-type, cordate prothallus is
formed. Rarely, the germ filament is branched (Fig. 16), with each branch
developing into separate gametophyte.
The mature prothallus is a typical heart-shaped structure with a prominent
apical notch and takes about 128 days to develop from spore. The young
gametophytes are entirely naked, being devoid of any hairs (Fig. 29). The
rhizoids are hyaline. Until this stage of development, the midrib is undifferentiated and the sex-organs are not formed.
DISCUSSION
The early gametophyte development in Lomariopsidaceae has been
classified primarily as Drynaria-type (Nayar and Kaur, 1971), or rarely the
Aspidium-type as in Elaphoglossum (Stokey and Atkinson, 1957). The
Drynaria-type of gametophyte development has been reported in a majority
of the genera of Polypodiaceae (Nayar and Raza, 1970; Nayar and Kaur, 1971;
Chandra, 1979; Chiou and Farrar, 1997; Perez-Garcia et al., 2001. This type of
development is also characteristic of some Athyrioideae, Cheiropleuriaceae,
Cyatheaceae, Dipteridaceae, Dryopteridaceae, Gleicheniaceae, Loxsomaceae,
Thelypterdiaceae, (Nayar and Kaur, 1971).
The present study reveals that spore germination in L. sorbifolia is the
typical Vittaria-type of polar germination, while prothallial development is
primarily of the Adiantum-type as reported for the Dennstaedtiaceae (Nayar
and Kaur, 1969). The Adiantum-type of prothallial development is characteristic of the families Dennstaedtiaceae, Grammitidaceae, Hypolepidaceae,
Lindseaceae, Lygodiaceae and Plagiogyriaceae. In addition, it is also found
in some genera of Cyatheaceae, Athyrioideae, Adiantaceae (Adiantum,
Coniogramme) and occasionally of the families Dryopteridaceae (Didymochlaena), Aspleniaceae (some species of Asplenium), Blechnaceae (some
species of Blechnum) and Cheilanthaceae (Doryopteris, some species of
Cheilanthes) (Nayar and Kaur, 1969, 1971).
Lomagramma sorbifolia is unusual, so far as the development of the
gametophyte (Adiantum-type) is concerned, relative to most of the other
genera of the Lomariopsidoid ferns. However, it shows similarities with other
30
AMERICAN FERN JOURNAL: VOLUME 93 NUMBER 1 (2003)
members of the Lomariopsidoid group, which have a Drynaria-type of
development. The Adiantum-type of development has been considered to be
more primitive than that of the Drynaria-type. In the Adiantum-type of
development, growth and expansion of the prothallus is mainly through the
activity of meristematic cells, whereas in the Drynaria-type of development the
meristematic cells do not play a very active part in the growth and expansion
of the young prothallus, as is the case for the majority of the Polypodiaceae
(Nayar 1962, 1963, 1965).
Strap-shaped, lobed, or elongated prothallii (Atkinson, 1973), as reported in
some of the Lomariopsidaceae (Lomariopsis hederacea, Egenolfia vivipara,
Bolbitis repanda and Elaphoglossum cuspidatum), have not been observed in
L. sorbifolia. The prothallus is naked throughout as reported for most species
of Bolbitis and Elaphoglossum. The spores are bilateral and non-perinate as in
Thysansoria (Nayar and Kaur, 1965).
However, at least in some cases of L. sorbifolia, besides the Drynaria-type
of early gametophyte development, the most common development is of
Adiantum-type. Nayar and Kaur (1969) consider this an unusual feature among
most of the other genera of the lomariopsidoid ferns. This supports the view of
Holttum (1947), who considers them possibly to have been derived directly
from a dennstaedtioid stock.
ACKNOWLEDGMENTS
We are grateful to Professor B. K. Nayar, ex Head, Department of Botany, Calicut University,
Kerala, India for valuable suggestions and advice. We also acknowledge with gratitude to Dr. P.
Pushpangadan, Director, N.B.R.I., Lucknow (INDIA) for constant encouragement and the laboratory
facilities for this work. Mrittunjai Srivastava is grateful to Department of Science & Technology,
New Delhi for the award of Research Associate Fellowship.
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